import java.util.Scanner;

public class Exer345 {
    public static void main(String[] args) {
        System.out.println("请输入要购买钢管的长度：");
        Scanner input = new Scanner(System.in);
        double length = input.nextDouble();
        if((int)length%3==0){
            System.out.println("需要购买" + (int)length/3 + "根钢管");
        }else{
            System.out.println("需要购买" + ((int)length/3+1) + "根钢管");
        }

    }
}


